The present invention relates to a radio communication apparatus consisting of a base station a plurality of portable units disposed around the base station and, possibly a relay unit connecting the base station with at least one portable unit, and more particularly, to a monitoring system for a radio communication apparatus for monitoring the operation of the portable unit and relay unit through the base station.
Conventionally, in a radio communication apparatus of this kind the respective operations of the portable unit and the relay unit are cyclically monitored through the base station for a predetermined period in a polling manner. Namely the base station transmits an inquiry signal to each of the portable (or relay) units and then the portable (or relay) unit, which receives the inquiry signal, replies by sending an answer signal to the base station. This answer signal includes information of the operation states of the unit, i.e.. normal or abnormal states of respective circuitry parts. After the reception of the answer signal and the execution of a preprogrammed treatment responsive to the answer signal, the base station sequentially transmits the inquiry signal to another unit. If the base station does not receive an answer signal from a unit within a predetermined period (e.g.,a few seconds) after transmitting the inquiry signal, then the base station determines that the unit is in trouble. In this case, the base station appropriately addresses the trouble and then transmits an inquiry signal to the next unit.
In the aforementioned monitoring system of the prior art, however, the base station transmits the inquiry signal to each unit for a relatively short time period. Consequently each unit transmits the answer signal indicating its state to the base station for such a short time period. According to this system, the unit has to respond to the base station if its operation state is normal. In this case. each unit is frequently accessed and required to respond for monitoring purposes. Therefore, this monitoring operation wastes power, which is a serious problem especially if the portable (or relay) unit is powered by a battery and is located in remote rural areas.